Faith's past is a mystery. Very few details have been brought up. We know that she was in an apparent paramilitary organization against her will in Brazil. This was the time that they worked on her power, making her stronger.
Her first appearance was in the Obsidian Age storyline of the JLA when the JLA went back in time and were defeated. The story arc showed some flirtatiousness with Green Arrow and Nightwing though both were just to tease. Her powers shown included flight, healing and telekinesis. She saved Zatanna from an ancient Atlantean socceress. Eventually the JLA tricked the witch and defeated her with the help of Aquaman.
Faith's next appearance came during a cosmic war. Faith helped the team by saying that there is no good or evil, it's all just what you wish. Faith then demonstrated how powerful she is by easily crippling the flagship of the enemy. Faith then showed what could be the true extent of her powers by singlehandedly destroying the whole fleet of ships before passing out.
Faith's last appearance in the JLA as a league member was in the Tenth Circle where she is attacked by Superman and brought to a vampire who then bites her. After this role she went to the Doom Patrol, where she was going to help a young girl who went by the codename " Nudge" learn more about controling her powers. During the CSA storyline Faith came back to help the JLA.